Method facilitating inter-mode handoff

ABSTRACT

A cellular handset supports non compressed handover for different frequency ranges, and different wireless standards.

BACKGROUND

Cellular phones (handsets) are increasing in complexity as handsetsincorporate more types of service. In most of the world, the trend isfor a handset to work with both Code Division Multiple Access (CDMA)type signals as well as the older Frequency Modulation (fm) typesignals. These different modulation schemes both coexist in the samesignal band and exist in different bands. The handset may have totransition from one to the other.

There are four major GSM standards as shown in Table 1. The low bandcontains two standards: GSM 850 and GSM 900. The high band also containstwo standards: GSM 1800 and GSM 1900. GSM 850 operates in the UnitedStates, in the cellular band. GSM 900 operates in Europe. GSM 1800, alsoknown as DCS, also operates in Europe. GSM 1900 operates in the UnitedStates in the PCS band. The modulation scheme WCDMA operates in most ofthe world (with the US the major exception), in the UMTS band. TABLE 1Standard Transmit Receive GSM 850 824 to 849 MHz 869 to 894 MHz GSM 900890 to 915 MHz 935 to 960 MHz GSM 1800 1710 to 1910 MHz 1805 to 1880 MHzGSM 1900 1850 to 1910 MHz 1930 to 1990 MHz UMTS 1920 to 1980 MHz 2110 to2170 MHz

Global System for Mobile Communications (GSM) type phones are becomingthe defacto global standard. Consequently, handsets that enable the GSMscheme must also support other schemes. To illustrate, 3^(rd) Generation(3G) handsets must support both GSM and WCDMA. Both modes operatesimultaneously, communicating in one mode and searching for service inanother. Prior art architecture requires timing to avoidself-interference. This timing technique is called “Compressed Mode”(CM). In CM, the UMTS transmitter is temporarily switched into a stateof twice the data rate, and thus twice the power. This allows for afollowing state where this transmitter is not broadcasting. The handsetis then set to receive either GSM band, in order to establish a reliablelink to a GSM basestation. This allows the handset to hand-over into theGSM network in a reliable manner. There is a price to be paid for thismode, however. First, this requires that the handset double it's outputpower. This is not possible if the handset is at the far end of it'srange. Indeed, the most likely time for such a hand-over is just such acircumstance. Second, this increase in power results in a variable powerat the basestation, impacting the network's power control. Loss of powercontrol impacts the network capacity.

FIG. 1 shows a prior art Quad Band Dual Mode (QBDM) handset whichrequires compressed mode handover. Current 3G front-end circuits consistof two main components: the switch and the filters. The switch togglesbetween transmission (Tx) and reception (Rx) in either GSM mode or tothe duplexer for the WCDMA in the UMTS band. The antenna switchdetermines which path is connected to the antenna. For GSM, either thetransmitter or the receiver is engaged. For WCDMA, both Tx and Rx are onconcurrently and must be kept distinct with a duplexer. In most of theworld, the handset can operate in three modes: GSM 900, GSM 1800, orWCDMA. In the US, where the UMTS band is not allowed, the handset canoperate in either GSM 850 or 1900.

FIG. 2 shows another prior art QBDM handset that supports compressedmode handover. Similar to FIG. 1, the switch toggles betweentransmission (Tx) and reception (Rx) in either GSM mode or to theduplexer for the WCDMA in the UMTS band. After the antenna receives thesignal, the signal path is split into two by the diplexer. Positioned oneither side of the diplexer are switches that further determine whichpath is connected to the antenna. For GSM, either the transmitter or thereceiver is engaged. For WCDMA, both Tx and Rx are on concurrently andmust be kept distinct with a duplexer. The handset can operate in threemodes: GSM 900, GSM 1800, or WCDMA. While supporting non compressed modein GSM 900, this architecture also supports only CM handover in GSM1800. Similarly, there is no handover to the US GSM bands.

FIG. 3 shows another prior art QBDM handset with compressed modehandover. This circuit requires careful design as the phase must beright for all of the filters. The handset supports non-compressed modehandover from WCDMA to only GSM 900. Handover to GSM 1800 requirescompressed mode. In addition, there are four different states possible,one for each switch state. All present different impedances in the UMTSRx band. The differing impedances make it difficult to properly tune thereceiver, reducing sensitivity in some states, possibly increasing thenumber of frame errors. The handset itself counts upon the receivedsignal to estimate the distance to the base station. The change inimpedance will introduce error into this calculation, impacting thequality of the link.

SUMMARY

In a circuit topology, a handset that supports GSM 900, GSM 1800/, UMTS,and may or may not support GSM 850 or GSM 1900, includes an antenna fortransceiving a signal. A diplexer interposes the antenna, a firstantenna switch and a second antenna switch. A first transmitter for afirst frequency band connects to an output of the first antenna switch.A first receiver for the first frequency band connects to another outputof the first antenna switch. A second transmitter for a second frequencyband connects to an output of the second antenna switch. A triplexer hasan input connected to another output of the second antenna switch. Thetriplexer has a first output connected to a receiver at the secondfrequency band, a second output connected to a receiver at the thirdfrequency band, and a third output connected to a transmitter of thethird frequency band.

In an alternate circuit topology, the first antenna switch furtherincludes a third output connected to a second receiver for a thirdfrequency band. The second antenna switch further includes a thirdoutput connected to a second receiver for a fourth frequency band.Including transmit bands for GSM 850 and GSM 1900 does not require extraswitches. The power amplifiers for GSM are wide band, and so the GSM 900transmitter will also cover the 850 band, the GSM 1800 transmitter willcover the 1900 band.

In another circuit topology, an antenna transceives a signal. An antennaswitch, connected to the antenna, has outputs connected to a firsttransmitter for a first frequency band, a first receiver for the firstfrequency band, a second receiver for a second frequency band, a secondtransmitter for the second frequency band, and a quadplexer. Thequadplexer has outputs connected to a receiver in the first frequencyband, a receiver in the second frequency band, a receiver in the thirdfrequency band, and a transmitter of the third frequency band.

This topology can be generalized to an n-plexer, or an arbitrary numberof filters connected to discriminate between an arbitrary number offrequencies. This is limited in practice by the bands that an antennacan cover, and the separation of the frequencies. Typical handsetantennae cover all the bands discussed above, as well as perhaps GPS(Global Positioning Satellite) at 1575 MHz. Thus, one could discriminatebetween two GSM receive bands, both transmit and receive frequency bandsof UMTS, and the GPS band, for a 5-plexer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a circuit topology for a prior art handset.

FIG. 2 illustrates a circuit topology for a prior art handset.

FIG. 3 illustrates a circuit topology for a prior art handset.

FIG. 4 illustrates a circuit topology according to the presentinvention.

FIG. 5 illustrates an alternate circuit topology according to thepresent invention.

FIG. 6 illustrates a triplexer according to the present invention.

FIG. 7 illustrates an alternate triplexer according to the presentinvention.

FIG. 8 illustrates the frequency response of the triplexer shown in FIG.7

FIG. 9 illustrates an alternate circuit topology of the presentinvention.

FIG. 10 illustrates a quadplexer of the present invention.

FIG. 11 illustrates a frequency response for the quadplexer shown inFIG. 10.

DETAILED DESCRIPTION

A cellular handset supports simultaneous service for different frequencyranges and different wireless standards.

FIG. 4 illustrates an embodiment (10) of the present invention. Anantenna (12) is connected to a diplexer (14) having a first and a secondoutput (14A, 14B). The first diplexer output (14A) connects to a firstsingle pole two-throw switch (SP2T) (16). The first SP2T (16) isconnected to a GSM 850 transmitter (18) and an optional bandpass filterfor GSM 900 receiver (19). The bandpass filter for GSM900 receive (19)is further connected to a GSM900 receiver (20). The second diplexeroutput (14B) connects to a second SP2T (22). The second SP2T (22)connects to a GSM 1800 transmitter (24) and a triplexer (26). Thetriplexer (26) has a first output (26 a) connected to a GSM 1800receiver (28), a second output (26B) connected to UMTS band receiver(30), and a third output (26C) connected to a UMTS band transmitter(32).

In operation, this circuit topology supports non compressed modehand-over from UMTS to either GSM 1800 or GSM 900.

FIG. 5 illustrates another embodiment (10′) of the present invention. Anantenna (12) is connected to a diplexer (14) having a first and a secondoutput (14A, 14B). The first diplexer output (14A) connects to a firstsingle pole three-throw switch (SP3T) (34). The first SP3T (34) isconnected to a GSM 850/900 transmitter (36), an optional bandpass filterfor GSM 900 receive (19), and an optional bandpass filter for GSM 850(37). The bandpass filter for GSM 900 receive (19) is further connectedto a GSM 900 receiver (20). The bandpass filter for GSM 850 receive (37)is further connected to a GSM 850 receiver (38). The second diplexeroutput (14B) connects to a second SP3T (40). The second SP3T (40)connects to a GSM 1800/1900 transmitter (42), a triplexer (26), and abandpass filter for GSM 1900 receive (43). The bandpass filter for GSM1900 receive (43) further connects to a GSM 1900 receiver (44). Thetriplexer (26) has a first output (26A) connected to a GSM 1800 receiver(28), a second output (26B) connected to UMTS band receiver (30), and athird output (26C) connected to a UMTS band transmitter (32).

In operation, this circuit topology supports non compressedmode-hand-over from UMTS to either GSM 1800 or GSM 900.

FIGS. 6, 7, and 10 illustrate embodiments of an n-plexer according tothe invention. Each filter has an impedance that varies greatly withfrequency. In the pass band, the filter looks like a low loss path, andso the impedance on one port appears on the other, and vice versa. Inthe reject bands, the filter looks like either an open circuit, or ashort circuit, depending upon the port, and the filter implementation.To illustrate, in FIG. 7, the UMTS Rx filter presents a short circuit atthe UMTS Tx band. This short circuit is rotated by the transmission linebetween the two UMTS filters such that the short circuit becomes an opencircuit, and so does not load the signal at UMTS Tx. The UMTS Tx filtersimilarly looks like a short circuit at GSM 1800. The transmission linebetween the UMTS Tx filter and the GSM 1800 filter rotates this shortcircuit into an open circuit.

FIG. 6 illustrates a triplexer (26) of the present invention. An inputis connected to a first transmission line (46) and a first bandpassfilter at a first frequency band (48). The first transmission line (46)is further connected to a second transmission line (50) and a secondbandpass filter at a second frequency band (52). The second transmissionline (50) connects to a third bandpass filter at a third frequency band(54). In a preferred embodiment, the first frequency band is a GSM 1800,the second frequency band is UMTS transmit, and a third frequency bandis a UMTS receive, as shown in FIG. 4 and FIG. 5.

FIG. 7 illustrates an alternate triplexer (26) of the present invention.An input is connected to a first and a second transmission line (56,58). The first transmission line (56) is connected to a first bandpassfilter at first frequency band (48) and a second bandpass filter at asecond frequency band (52). The second transmission line (58) isconnected to a third bandpass filter at a third frequency band (54). Ina preferred embodiment, the first frequency band is GSM 1800 receive,the second frequency band is UMTS transmit, and a third frequency bandis a UMTS receive.

FIG. 8 illustrates the frequency response of the triplexer (26, 26′).

FIG. 9 illustrates an alternate circuit topology (10″) of the presentinvention. An antenna (12) is connected to a single pole five throwswitch (SP5T) (60). The SP5T (60) connects to a GSM 850/900 transmitter(36), an optional bandpass filter for GSM 850 receive (37), an optionalbandpass filter for GSM 1900 receive (43), a GSM 1800/1900 transmitter(42), and a quadplexer (62). The bandpass filter for GSM 850 receive(37) further connects to a GSM 850 receiver (38). The bandpass filterfor GSM 1900 receive (43) further connects to a GSM 1900 receiver (44).The quadplexer (62) connects to a GSM 900 receiver (20), a GSM 1800receiver (28), a UMTS band receiver (30), and a UMTS band transmitter(32). The circuit supports non-compressed mode hand-over from UMTS toeither GSM 1800 or GSM 900.

FIG. 10 illustrates a quadplexer (62) of the present invention. Threetransmission lines (64, 66, 68) are connected at the input. A firstbandpass filter at a first frequency band (70) connects to the output ofthe first transmission line (64). A second bandpass filter at a secondfrequency band (72) connects to the output of the second transmissionline (66). A third bandpass filter at a third frequency band (74)connects to the output of the second transmission line (66). A fourthbandpass filter at a fourth frequency band (76) connects to the outputof the third transmission line (68). In a preferred embodiment, thefirst frequency band is GSM 900 receive, the second frequency band isGSM 1800 receive, the third frequency band device is UMTS transmit, anda fourth frequency band is UMTS receive.

FIG. 11 illustrates a frequency response for the quadplexer (62) shownin FIG. 10.

1. A handset supporting difference frequency bands comprising: anantenna transceiving a signal; a diplexer connected to the antennahaving a first and a second diplexer output; a first antenna switch,connected to the first diplexer output, having a first and a secondoutput; a first transmitter for a first frequency band connected to thefirst output of the first antenna switch; a first receiver for the firstfrequency band connected to the second output of the first antennaswitch; a second antenna switch, connected to the second diplexeroutput, having a first and a second output; a second transmitter for asecond frequency band connected to the first output of the secondantenna switch; and a triplexer, connected to the second output of thesecond antenna switch, having a first output connected to a receiver atthe second frequency, a second output connected to a receiver at thethird frequency band, and a third output connected to a transmitter ofthe third frequency band.
 2. A handset as in claim 1, wherein the firstfrequency band is GSM
 900. 3. A handset as in claim 1, wherein thesecond frequency band is GSM
 1800. 4. A handset as in claim 1, whereinthe third frequency band is UMTS.
 5. A handset as in claim 1, furthercomprising: the first antenna switch having a third output; a receiverfor the fourth frequency band connected to the third output of the firstantenna switch; the second antenna switch having a third output; and areceiver for the fifth frequency band connected to the third output ofthe second antenna switch.
 6. A handset as in claim 5, wherein thefourth frequency band is GSM
 850. 7. A handset as in claim 5, whereinthe fifth frequency band is GSM
 1900. 8. A handset as in claim 5,wherein the third frequency band is UMTS.
 9. A handset, as in claim 1,the triplexer including: a first bandpass filter connecting to thereceiver for the second frequency band; a first transmission line,connected to the first bandpass filter; a second bandpass filterconnecting to the transmitter in the third frequency band; a secondtransmission line, connected to the second bandpass filter and firsttransmission line; and a third bandpass filter connecting to thereceiver in the third frequency band; wherein transmission lines arechosen to appropriately rotate the reject band impedances to opencircuits as required.
 10. A handset as in claim 1, the triplexerincluding: a first transmission line; a first and a second bandpassfilter connecting to the first transmission line, wherein the firstbandpass filter passes the second frequency band and the second bandpassfilter passes the third frequency band; a second transmission lineconnecting to the first transmission line; and a third bandpass filterconnecting to the second transmission line, for passing the thirdfrequency band; wherein the second transmission line is chosen toappropriately rotate the reject band impedance of the third bandpassfilter into an open circuit at the passband of filters one and two. 11.A handset comprising: an antenna transceiving a signal; an antennaswitch, connected to the antenna, having a first, a second, a third, afourth, and a fifth output; a first transmitter for first and fourthfrequency bands connected to the first output; a first receiver for thefirst frequency band connected to the second output; a second receiverfor a fifth frequency band connected to the third output; a secondtransmitter for the second and fifth frequency bands connected to thefourth output; a quadplexer, connected to the fifth output, havingoutputs connected to a receiver in the first frequency band, a receiverin the second frequency band, a receiver in the third frequency band,and a transmitter of the third frequency band.
 12. A triplexerincluding: a first transmission line; a first and a second bandpassfilter connecting to the first transmission line, wherein the firstbandpass filter passes a first frequency band and the second bandpassfilter passes the second frequency band; a second transmission lineconnecting to the first transmission line; and a third bandpass filterconnecting to the second transmission line, for passing the secondfrequency band; wherein the second transmission is chosen toappropriately rotate the reject band impedance of the third bandpassfilter into an open circuit at the passband of filters one and two. 13.A n-plexer including: a first and a second transmission line connectedat an input, each having an output; a first and a second bandpassfilter, each connected to the output of the first transmission line, thefirst bandpass filter passing a first frequency band, the secondbandpass filter passing a second frequency band; and a third bandpassfilter, connected to the output of the second transmission line, forpassing the second frequency band.
 14. A n-plexer, as defined in claim13, further including: a third transmission line, connected at theinput, having an output; a fourth bandpass filter, connected to theoutput of the third transmission line for passing a third frequencyband.